Stabilization of CCA-contaminated soil with iron products - a field experiment

Abstract

Chemical stabilization of metals is lately considered as a possible pretreatment for soilcontaminated with average levels of trace elements. The element mobility in soil can bealtered by adding soil amendments that can adsorb, complex, or co-precipitate trace elements.As a consequence, pollutant spreading from the contaminated soil and effect on the recipientcan be reduced. The different contaminants originating from wood impregnation chemicals,e.g. Cu, Cr, and As limit the choice of amendments because e.g. large pH fluctuations andconsequent mobilization of Cu or As should be avoided. The results show that the leaching ofarsenic is lowest in the lysimeter with 15% Fe3O4. In both lysimeters with untreated soil andwith 1 % Fe 0, the arsenic leaching seems to decrease with the sampling depth. The leaching ofcopper is generally low. Further the addition of iron seems to increase the leaching ofmanganese and nickel but to reduce the leaching of zinc. Results from the laboratoryexperiment show that the arsenic content in the leachate is lowest with the highest mixture ofmagnetite. Mixing is one of the key issues when discussing the treatment efficiency andpossible use of the treated soil. The results so far indicate that magnetite can be used fortreatment of CCA contaminated soil also at a large scale. Reduction of both arsenic andcopper using a single amendment is challenging as they behave opposite. Magnetite seems tobe a promising amendment even though a high amount of amendment needs to be added.Moreover, the potential establishment of reducing conditions at larger depths in the soil is ofconcern since this might lead to a rapid increase in arsenic leaching